Angioplasty procedures are widely recognized as efficient and effective methods for treating types of vascular disease. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, although it is also used for the treatment of stenoses in other parts of the vascular system.
Apparatus for conducting angioplasty procedures generally include an inflatable balloon at their distal end. Typically in coronary procedures, a hollow guide catheter and/or guide wire are used in guiding the dilatation catheter through the vascular system to a location near the stenosis. Using fluoroscopy, assisted by the guide wire, the physician guides the dilatation catheter the remaining distance through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying fluid under pressure through an inflation lumen in the catheter to the balloon. The inflation of the balloon causes widening of the lumen of the artery to reestablish acceptable blood flow through the artery.
An over-the-wire (OTW) catheter design is well known in the art. The over-the-wire catheter is a catheter in which an inner tubular member, whether integral as in a multi-lumen tubular member or separate as in a coaxial design, provides a guide wire lumen so that the guide wire can provide a path to the stenosis, which may be tracked by the catheter as it is slidably received over the guide wire. In an over-the-wire design, the inner tubular member extends over the entire length of the catheter, and the lumen extending therethrough is isolated from the inflation fluid utilized to inflate the balloon.
Vascular occlusions to be treated by a balloon angioplasty apparatus can vary dramatically in size or length. With the variation in length of the occlusion, the area to be treated correspondingly varies in length. It is recognized as desirable to match the length of the balloon to be inflated during treatment as closely as possible to the length of the occlusion to be treated. This prevents expanding the balloon and pressing against a healthy artery wall. This requires, during a treatment, that the physician have on hand several catheters having different length balloons mounted thereon. It may also require the physician to exchange catheters in the middle of the treatment process so that a catheter of proper balloon length can be utilized. These factors can increase the cost of the procedure along with the time required for treatment.
The above problems can be overcome by incorporating a variable length balloon in a single dilatation catheter which allows selecting the length of the balloon at the time of or during treatment. Fogarty et al. (U.S. Pat. No. 4,564,014) and Saab (U.S. Pat. No. 5,246,421), the disclosures of which are incorporated herein by reference, disclose catheters incorporating a variable length balloon in a dilatation catheter.
Fogarty et al. discloses a catheter including an elongate elastomeric tube closed at its distal end and extending the full length of the catheter. A telescopic sheath is received around the elastomeric tube, which has a distal primary section which is moveable relative to the elastomeric tube and a proximal secondary section secured against movement relative to the elastomeric tube. A guide wire is disposed within and extends through the full length of the elastomeric tube with the guide wire having its distal end secured to the distal end of the tube, and proximal end extending from the proximal end of the tube. The length of the balloon is thus adjusted by moving the distal primary section of the sheath while maintaining the position of the elastomeric tube and proximal secondary section of the sheath.
To facilitate movement of the primary sheath section relative to the elastomeric tube, Fogarty et al. disclose that the elastomeric tube may be stretched lengthwise to reduce its diametrical cross-section by extending the guide wire which is fixed to the distal end of the elastomeric tube. The fixing of the guide wire to the distal end of the elastomeric tube, although aiding in adjusting the size of the balloon, prevents use as an over-the-wire device. Further, the movable primary sheath portion of Fogarty et al., if adjusted after insertion into the vessel, must be moved and in contact with the vessel wall to be treated. This may restrict or hinder movement of the sheath.
Saab also discloses an adjustable-length balloon dilatation catheter apparatus incorporating an adjustable sheath which is externally manipulated to partially surround and contain the dilatation balloon segment of the catheter while the catheter balloon segments are expanded during a treatment procedure. Saab discloses an adjustable sheath which is substantially coaxial with the catheter and substantially surrounds the catheter body, balloon, and catheter tip. Saab discloses that the sheath may run the full length of the catheter or be provided at the distal end of a relatively stiff, control catheter, with the latter being coaxially mounted relative to the balloon catheter. Thus, the sheath of Saab includes a separate tubular member to provide the sheath.
A known limiting factor for utilizing over-the-wire catheters is the profile of the balloon and shaft relative to the blood vessel lumen size being treated. Thus, there has been a continuing effort to reduce the balloon profile and shaft size of the dilatation catheter so that the catheter can reach and cross a very tight stenosis or a stenosis in a small vessel. Over-the-wire catheter designs have particularly been noted as limited due to a larger profile relative to other catheter designs, such as fixed wire devices or single operator exchange devices. This limitation is due to the need for a separate guide wire lumen running the full length of the catheter which is separate from the inflation lumen.
Although Saab discloses that the catheter of his invention can be modified or tuned to be compatible with virtually any catheter construction including, but not limited to, over-the-wire catheters, such modifications would compound the problems with profile. To modify Saab would require adding a tubular sleeve over the outside diameter of the outer tubular member of the catheter, and thus, increase the profile of the overall assembly.